In the measuring housing provided with a gas inlet and a gas outlet, intelligent gas meters generally contain: two flexible measuring chambers filling in alternation to measure the volume of the gas flowing through, including the control system for the same, a counting device, components for remote querying regarding the counter status, and components for remote switching off/on of the gas flow. A remote switching is, for example, necessary for prepay systems or for disabling the gas meter on the part of the gas supplier. A shut-off valve at the gas inlet, the actuator of which is electrically actuated, functions for this purpose. In the interests of a most compact construction, reduction of working noises, and increase of manipulation safety, the shut-off valve, including its integrated power supply, is usually accommodated in the housing interior of the gas meter. From this fact arise the demands for the smallest dimensions of the shut-off valve, a high operating safety, and a long-term freedom from maintenance, among which demands, in particular, a long-lasting battery-supported mode of operation is also included. The latter requires, in particular, an extremely low energy consumption during switching of the shut-off valve and, if necessary, an improved protection against sparking at the actuator of the shut-off valve.
In contrast to actuators based on solenoid drives, actuators based on specialized electric motors have penetrated the market due to an improved manipulation safety against external influences generated by others; such actuators are largely impervious to wanton strikes, vibrations, and other types of manipulations.
From US2015/0060711 A1, by the same assignee, a shut-off valve with a shut-off body is known which is flange mounted within the gas meter at the gas supply connection, is designed as longitudinally displaceable with respect to a valve seat provided with a lip seal, in that the shut-off body sits on a control rod which is rotatably fixed and longitudinally moved in the valve housing. In the lower part, the control rod forms, with an adjusting nut element, a nut-spindle drive via which the shut-off body allows or shuts off a gas flow through the shut-off valve, depending on the rotational direction of the adjusting nut element. The adjusting nut element is driven by a small direct current motor via a multistage gear transmission.
The gas shut-off valve according to US2015/0060711 A1 has a device limiting the torque of the energized small direct current motor in the shut-off position and/or in the open position of the valve in the form of a purely mechanical torque limiting device, in that, after traveling a predefined travel distance, the control rod disengages from the adjusting nut element and the latter then rotates freely. The travel distance is thus not readjustable without disassembly work.
By using stepper motors, corresponding, for example, to EP 0 836 701 B1 or U.S. Pat. No. 6,129,105, defined travel distances may be implemented using a step specification which is changeable via software; however, stepper motors are comparatively large, expensive, and substantially more complex to control than, e.g. small direct current motors with comparable output. The design of the disclosed shut-off bodies is, in addition, complex from a design-view and demands, due to safety and functionality, a very precise control in order to properly reach the valve seat of the sealing body over the long term.
By using economical miniature direct current motors with a predefined runtime control for shutting off or opening, the problem which has previously emerged is that the direct current motors change their working point depending on the load, and thus the actual opening/closing time of the valve changes during operation, for example, caused by gas pressure or temperature fluctuations. To ensure a complete opening/closing, the small direct current motors were therefore energized significantly longer than would actually be necessary, wherein the shut-off body moves hard up to the stop of the valve seat. For additional safety, multiple seconds are also generally specified, for example, to take fluctuations of the gas pressure into account. In valves with flat seals, which require a high sealing force due to design considerations, the shut-off body therefore moves into the valve seat until the direct current motor is blocked. The direct current motor receives in this state its maximum electrical load until the valve is switched off in a time-controlled way. During the relatively long energizing time, the energy consumption is obviously high, which significantly stresses the battery for power supply, whose service life is significantly reduced, and the motor service life is reduced due to the maximum power flow across the brushes. Furthermore, a jamming of the adjustment components caused by the high compression force may not be reliably excluded during the usual operating conditions (longer inactivity, dropping battery voltage) and environmental conditions (temperature fluctuations from −20° C. to +50° C., air pressure fluctuations).